The present invention relates generally to the control of machine operation by computer and more particularly to a system for controlling in real time a plurality of satellite automatic machines by a remotely located process control computer. The computer is connected electrically to all of the machines simultaneously by a common data bus.
Controlling the operation of individual machines automatically is well known in the art. Generally instructions for a particular operation or operational sequence of the machine are fed directly to the machine from an input device, e.g. a card or tape reader, located at the machine site. This method requires at each machine not only the input device which reads and decodes instructions from a prepared program of instructions but also storage at the machine of the desired program whether contained in cards, tape, magnetic memory, etc. U.S. Pat. No. 3,793,625 is an example of this type of system. Where the machine continuously and repetitively performs the same or a few similar tasks, e.g. a drill press, the programmed instructions are readily stored at the machine site. However, where a machine is suited to produce a wide variety of products e.g. a circuit board wiring machine capable of producing a multitude of wiring patterns as instructed, the number of programmed instructions which must be stored or provided at the machine site can be substantial. Also the mechanics of changing programs can require considerable operator skills, attention and program handling at the machine, with the contingent cost and risks of damage to the instructions, i.e. cards, tapes, etc. Additionally there is the initial cost and maintenance costs of providing independent input and data storage files at each machine.
Control concepts have also been directed toward the operation of a plurality of similar machines from instruction programs maintained in a single central memory and distributed to the machines by a central processing computer unit. U.S. Pat. No. 3,760,169, Interface System For Direct Numeric Control of Automatic Wiring Machines is an example of such a system. Therein when so requested by an individual machine, a process control computer retrieves blocks of instruction data from stored memory and outputs the instructions on a data highway, as it is called in the terminology of said patent.
The data highway provides a common path from computer to all machines with a parallel branch from the common bus extending to each machine via an independent interface unit. Individual control units, one associated with each machine, request data from the computer in a format which identifies the machine requesting service. The computer decodes the incoming request and outputs a data block from memory responsive to said request. At the same time the computer provides a ground line which enables reception of the data only at the machine which has requested data. The control unit reads a portion of the outputted data block to ascertain that the computer outputted data is valid for the machine and to allow the interface unit to accept data.
This system although using a plurality of common data highways is nevertheless complex in that it requires a control unit and an interface unit at each machine, as well as two common data highways, one between the computer and the interface units and another data highway between the computer and the control units. Further there are individual wiring lines dedicated to interconnecting (a) each machine to its associated interface unit, (b) each interface unit to its associated control unit, (c) each interface unit to the computer, and (d) each control unit to the computer. As configured the computer serves merely as a data retrieval and distribution control console. The machine itself is not computer controlled but is in fact controlled in its operations by the interface unit which controls the computer, stores data and feeds additional instruction steps to the machine as the machine performs and completes each of its electro-mechanical operations.